Hi Archie, well I know that when I first looked at 3cx in November last year, version 3.1 didnt support DNS SRV, but when version 5 came out I notice it did. I only know his from the logs at he VOIP provider. So just to show you i've loaded up version 5 onto a second machine, see below the two logs of version 5 and version 5.1 which clearly show. Maybe 3cx is unwitingly supporting SRV in version 5.0 without you knowing.